The present invention relates to a tire press and more particularly to an improvement in a vertical tire press.
A vertical tire press of a type such that an upper mold is vertically moved to be opened and closed with respect to a lower mold is disclosed in U.S. Pat. No. 4,563,139 and U.S. Pat. No. 4,686,129. Referring to FIG. 10 which shows the vertical tire press disclosed in this prior art, a hydraulic cylinder 148 having a short piston stroke necessary for applying a mold clamping pressure is provided at a bottom portion 126 of a lower mold shell 125. The lower mold shell 125 is resiliently supported by a spring 127 onto a press base 128. A lower mold assembly consisting of a platen support, a heat insulator 130a, a platen 133 and a mold 112 is fixed through a plurality of connecting support rods 131 to the press base 128.
An upper mold shell 121 is provided with means for vertically moving an upper mold assembly through a mold height adjusting screw cylinder threadedly engaged with a mold height adjusting nut 136 located at a central position of a top portion of the upper mold shell 121. The upper mold shell 121 is vertically movable by the rotation of a screw provided at press frame posts on opposite sides of the press base 128.
In operation, the upper mold shell 121 is closed with respect to the lower mold shell 125, and both the shells are locked by a breach ring 135. Then, the hydraulic cylinder 148 is operated to lower the assembly of both the shells 121 and 125 and thereby clamp the upper mold assembly to the lower mold assembly. Then, a heat/pressure medium such as steam is supplied through a central mechanism to a green tire. Thus, vulcanization of the green tire is carried out under the pressure with heat of the steam with the upper and lower molds maintained firmly clamped.
In the event that hydraulic pressure of the hydraulic cylinder 148 is reduced for any reason, the upper mold is opened upwardly by the pressure supplied into a molding bladder in the green tire, and the upper and lower mold shells 121 and 125 are lifted until a clearance becomes zero. That is, the upper mold is restrained from being opened over the clearance. Accordingly, the bladder and the tire are prevented from being forced out from between the upper and lower molds.
Another example of the mold height adjusting device is disclosed in U.S. Pat. No. 4,669,964. According to this mold height adjusting device, four screw shafts are mounted to an upper mold supporting platen in such a manner as to surround a central mechanism at circumferentially equal intervals. An upper mold of an upper mold assembly is mounted to the upper mold supporting platen. The screw shafts project upwardly from a top portion of a dome, and are engaged with screw nuts provided on the top portion. Nut gears are associated with the screw nuts, and mesh with a center gear provided on the top portion of the dome. Thus, the upper mold is vertically moved according to a mold thickness.
The above-mentioned vertical tire press in the prior art is improved in alignment of the upper and lower molds, accuracy, uniformity of distribution of a mold clamping force, minimization of flex of the mold mounting surfaces, etc. However, the following problem is yet present.
As is appreciated from the above description, the prior art vertical tire press is of a so-called platen heating type such that a heat source is included in the platen or steam or the like is supplied to the platen, so as to heat the tire molds.
However, in the case of vulcanizing tires of a truck, bus, etc. and a large-scale tire of a special working vehicle, a sufficient heat cannot be applied to the tire molds in the platen heating type tire press. Therefore, it is necessary to directly supply a heat/pressure medium such as steam into a dome space defined by the upper and lower domes and strongly heat the tire molds.
In a dome type vertical tire press using a lock ring mechanism connecting the upper and lower domes to be clamped by the mold clamping cylinder, the lock ring mechanism requires a mechanical clearance, and a moving (sliding) clearance is necessary between the lower dome and the lower mold mounting member upon clamping the molds. Further, the mold height adjusting device provided at the tip portion of the upper dome also requires a mechanical clearance. Accordingly, there is a possibility that the heat/pressure medium supplied into the dome space will escape from these clearances, resulting in universal adoption of the platen heating type in the prior art vertical tire press.